Recent studies suggest that modifications in the number and function of nAChRs, by exposure to nicotine, plays an important role in the process of addiction. However, the molecular mechanisms important in regulating these receptors in the mammalian CNS remain poorly understood. In this grant we propose to address this question in Drosophila, a simple, genetically accessible model system. We have recently demonstrated that nAChRs, blocked by both curare and alpha-BTX, mediate the primary form of fast excitatory transmission between cultured Drosophila neurons, providing a unique opportunity to explore the genetic and biochemical signals important in regulation of these receptors and transmission at central cholinergic synapses. Our initial experiments will focus on characterization of the properties of the whole cell currents induced by acute exposure of cultured wildtype neurons to various concentration of nicotine. The second specific aim will examine the role of nicotine in regulation of the-functional nAChRs. Potential changes in the biophysical properties of these receptors will be assessed by monitoring the electrophysiological properties of nicotine-induced, ACh-induced, and cholinergic excitatory postsynaptic currents (EPSCs), following chronic exposure to nicotine. To determine if there are changes in the numbers of receptors, 125l-alphaBTX binding will be monitored before and after exposure to nicotine. In the third aim we will examine the effects of short duration, repetitive exposure to nicotine, mimicking the exposure that occurs during smoking, on nAChR expression. Finally, we will examine the properties of nicotine induced currents and regulation of nAChRs in neurons from dunce, a learning and memory mutant with defects in CAMP-signaling. Differences in the electrophysiological and pharmacological properties of the nAChRs and cholinergic synaptic currents between dunce and wildtype neurons will be important in determining if nicotine activates the same CAMP-signaling cascade that is important in reinforced learning paradigms in flies. The results of our studies will provide important insights into the molecular mechanisms underlying nicotine induced regulation of nAChRs. These data will also contribute to the general understanding of the molecular mechanisms important in regulating transmission at excitatory synapses, likely to be highly conserved between vertebrates and invertebrates, and therefore should aid in the design of drugs and/or therapies aimed at modulating plasticity in synaptic pathways contributing to addiction in humans.